JP7310585B2 - BALL SCREW NUT AND METHOD FOR MANUFACTURING BALL SCREW NUT - Google Patents

Description

The present invention relates to a ball screw nut and a method for manufacturing a ball screw nut.

A ball screw is known as a device that converts rotary motion into linear motion. A ball screw includes a screw shaft, a nut, and a plurality of balls. As an example of a ball screw nut, a nut is known that has a ball circulation groove (recess) that is a path for guiding balls from one end of a ball rolling path to the other end. The ball circulation groove is formed, for example, by pressing a convex mold having projections on the outer peripheral surface against the inner peripheral surface of the nut. Patent Literature 1 describes an example of a method for manufacturing such a nut.

JP 2014-62570 A

By the way, if the thickness of the portion of the nut corresponding to the ball circulation groove is small, it is difficult to increase the strength of the nut. On the other hand, as described in Patent Document 1, it is not easy to form a ball circulation groove in a portion corresponding to an annular member (stepped cylindrical portion) provided on the outer peripheral surface of the nut.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a ball screw nut and a ball screw nut manufacturing method that can improve the strength of the nut and easily form a ball circulation groove. The purpose is to

In order to achieve the above object, a ball screw nut according to one aspect of the present disclosure includes a cylindrical main body, a thread groove arranged on the inner peripheral surface of the main body, and a a ball circulation groove arranged and deeper than the thread groove; and a convex portion arranged on the outer peripheral surface of the main body portion, the ball circulation groove being arranged behind the convex portion and extending from the main body portion. The length of the protrusion in the circumferential direction is smaller than the length of the protrusion in the axial direction of the main body.

By arranging the ball circulation groove behind the projection, the wall thickness of the nut around the ball circulation groove is increased. That is, the distance from the surface of the ball circulation groove to the outer peripheral surface of the nut increases. Therefore, the strength of the portion of the nut surrounding the ball circulation groove is improved. As a result, when the nut is heat treated (quenched and tempered), the nut is less likely to be deformed, cracked, or the like. Further, since the length of the protrusion in the circumferential direction is smaller than the length of the protrusion in the axial direction, the ball circulation groove can be easily formed by forging even if the groove is arranged behind the protrusion. . Therefore, the nut of the ball screw can improve the strength of the nut and can easily form the ball circulation groove.

As a desirable aspect of the ball screw nut, the bottom of the ball circulation groove is arranged outside the outer peripheral surface of the main body in the radial direction of the main body.

As a result, the nut of the ball screw can be made thicker and smaller in the peripheral portion of the ball circulation groove of the nut.

As a desirable aspect of the ball screw nut, the length of the protrusion in the circumferential direction is smaller than the length of the ball circulation groove in the circumferential direction.

This makes it easier to form the ball circulation groove by forging even if the ball circulation groove is arranged on the back side of the projection. A ball screw nut can more easily form a ball circulation groove.

As a desirable aspect of the above ball screw nut, the convex portion has processing marks on its surface.

Forming the ball circulation groove becomes easier by providing the notch in the convex portion before forming the ball circulation groove. Machining traces are traces left on the surface of the protrusion due to the formation of the notch.

In order to achieve the above object, a ball screw nut manufacturing method according to one aspect of the present disclosure includes: A projection forming step of forming a projection smaller than the length, and a forging step of pressing a convex mold against the back surface of the projection to form a ball circulation groove.

By arranging the ball circulation groove behind the projection, the wall thickness of the nut around the ball circulation groove is increased. That is, the distance from the surface of the ball circulation groove to the outer peripheral surface of the nut increases. Therefore, the strength of the portion of the nut surrounding the ball circulation groove is improved. As a result, when the nut is heat treated (quenched and tempered), the nut is less likely to be deformed, cracked, or the like. In addition, since the length of the convex portion in the circumferential direction is smaller than the length of the convex portion in the axial direction, the ball circulation groove can be easily formed even when the ball circulation groove is formed by pressing the convex mold against the back surface of the convex portion. can. Therefore, the ball screw nut manufacturing method of the present disclosure can improve the strength of the nut and easily form the ball circulation groove.

As a desirable aspect of the method for manufacturing the nut of the ball screw, a cutting step of cutting a part of the convex portion is provided after the convex portion forming step and before the forging step.

By cutting a part of the convex portion before forming the ball circulation groove, it becomes easier to form the ball circulation groove. The ball screw nut manufacturing method of the present disclosure can form the ball circulation grooves more easily.

According to the ball screw nut and the ball screw nut manufacturing method of the present disclosure, the strength of the nut can be improved and the ball circulation groove can be easily formed.

FIG. 1 is a cross-sectional view of the ball screw of the embodiment. FIG. 2 is a perspective view of the nut of the embodiment. FIG. 3 is a perspective view of the nut of the embodiment. FIG. 4 is a front view of the nut of the embodiment. FIG. 5 is a cross-sectional view taken along line AA of FIG. Drawing 6 is a perspective view showing some nuts of an embodiment. FIG. 7 is a flow chart showing a method for manufacturing a nut according to the embodiment. FIG. 8 is a schematic diagram for explaining the method for manufacturing the nut of the embodiment. FIG. 9 is a schematic diagram for explaining the method for manufacturing the nut of the embodiment.

Hereinafter, the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, components in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate. Moreover, in the following embodiments, the same reference numerals are given to the same constituent elements as those described above, and redundant description may be omitted as appropriate.

(embodiment)
FIG. 1 is a cross-sectional view of the ball screw of the embodiment. FIG. 2 is a perspective view of the nut of the embodiment. FIG. 3 is a perspective view of the nut of the embodiment. 4 is a front view of the nut of the embodiment, and FIG. 5 is a sectional view taken along line AA of FIG. Drawing 6 is a perspective view showing some nuts of an embodiment. The ball screw 10 of this embodiment is a device that converts rotary motion into linear motion. The ball screw 10 is used, for example, in an electric actuator provided in a vehicle such as an automobile or a two-wheeled vehicle, or a ship. The ball screw 10 is applied not only to the electric actuator described above but also to various devices.

As shown in FIG. 1, the ball screw 10 includes a screw shaft 40, a nut 20, and balls 60. As shown in FIG. The screw shaft 40 has a thread groove 43 on its outer peripheral surface. The thread groove 43 is a spiral groove. The screw shaft 40 penetrates the nut 20 . The nut 20 has a thread groove 23 on its inner peripheral surface. The thread groove 23 is a spiral groove. A plurality of rolling paths 11 are formed between the thread groove 43 and the thread groove 23 . One rolling path 11 makes about one turn around the outer circumference of the thread groove 43 . A ball 60 is arranged on each of the plurality of rolling paths 11 .

As shown in FIG. 2 , the nut 20 includes a body portion 21 , thread grooves 23 , ball circulation grooves 25 and projections 27 . The body portion 21 is a cylindrical member. The thread groove 23 is arranged on the inner peripheral surface of the body portion 21 .

In the following description, the axial direction of the body portion 21 (the axial direction of the screw shaft 40 and the nut 20) is simply referred to as the axial direction. The radial direction of the body portion 21 (the direction perpendicular to the axial direction of the body portion 21) is simply referred to as the radial direction. The circumferential direction of the body portion 21 (the direction along the circle around the rotation axis Z of the screw shaft 40 and the nut 20) is simply referred to as the circumferential direction.

As shown in FIG. 5 , the ball circulation grooves 25 are arranged on the inner peripheral surface of the body portion 21 . The ball circulation groove 25 is deeper than the thread groove 23 . The ball circulation groove 25 is a substantially S-shaped groove provided on the inner peripheral surface of the body portion 21 . The ball circulation groove 25 is a groove connecting one end and the other end of one rolling path 11 . The ball circulation groove 25 returns the balls 60 from one end of one rolling path 11 to the other end. When the screw shaft 40 or the nut 20 rotates, the balls 60 endlessly circulate within the single rolling path 11 through the ball circulation grooves 25 .

In this embodiment, the number of ball circulation grooves 25 provided in the nut 20 is four. As shown in FIG. 4, the four ball circulation grooves 25 are arranged at different positions in the circumferential direction. When viewed from the axial direction, the four ball circulation grooves 25 are arranged at regular intervals in the circumferential direction.

The convex portion 27 is arranged on the outer peripheral surface of the main body portion 21 . The convex portion 27 is a projection protruding radially outward from the outer peripheral surface of the main body portion 21 . As shown in FIG. 3, the length P1 of the protrusion 27 in the circumferential direction is smaller than the length P2 of the protrusion 27 in the axial direction. In this embodiment, the convex portion 27 is provided over the entire length of the body portion 21 (the entire length of the nut 20). The end surface of the convex portion 27 is arranged on the same plane as the end surface of the main body portion 21 . The convex portion 27 is a member sometimes called a key.

The convex portion 27 is used, for example, as a member for preventing rotation of the nut 20 or as a guide member for guiding axial movement of the nut 20 . The protrusion 27 is arranged so as to fit into a recess or a guide groove provided in a member that supports the nut 20 . For example, the nut 20 is stopped from rotating and the nut 20 is guided in the axial direction by contacting the side surface (the surface facing the circumferential direction) of the convex portion 27 with the guide groove.

In this embodiment, the number of protrusions 27 provided on the nut 20 is four. As shown in FIG. 4, the four protrusions 27 are arranged at different positions in the circumferential direction. When viewed from the axial direction, the four protrusions 27 are arranged at regular intervals in the circumferential direction.

As shown in FIG. 4, the ball circulation groove 25 is arranged behind the convex portion 27 . When viewed from the radial direction, the ball circulation groove 25 overlaps the convex portion 27 . A length P1 of the protrusion 27 in the circumferential direction is smaller than a length P3 of the ball circulation groove 25 in the circumferential direction. A bottom 251 of the ball circulation groove 25 is arranged radially outside the outer peripheral surface of the body portion 21 . That is, as shown in FIG. 4, the distance L2 is longer than the distance L1 and shorter than the distance L3. A distance L1 is the distance from the rotation axis Z to the outer peripheral surface of the body portion 21 . A distance L2 is the distance from the rotation axis Z to the bottom 251 of the ball circulation groove 25 . A distance L3 is the maximum distance from the rotation axis Z to the surface of the projection 27 . The bottom 251 is arranged in the center of the ball circulation groove 25 in the circumferential direction. The depth of the ball circulation groove 25 is maximum at the center in the circumferential direction. The bottom 251 is arranged behind the thickest part of the projection 27 . When viewed from the radial direction, the bottom 251 overlaps the thickest portion of the convex portion 27 .

FIG. 7 is a flow chart showing a method for manufacturing a nut according to the embodiment. FIG. 8 is a schematic diagram for explaining the method for manufacturing the nut of the embodiment. FIG. 9 is a schematic diagram for explaining the method for manufacturing the nut of the embodiment.

As shown in FIG. 7, the method for manufacturing the nut 20 of the present embodiment includes a projection forming step S1. In the projection forming step S<b>1 , the projection 27 is formed by, for example, forging the cylindrical main body 21 . In the convex portion forming step S1, four convex portions 27 are formed on the outer peripheral surface of the main body portion 21 . It should be noted that, in the convex portion forming step S1, the convex portion 27 does not necessarily have to be formed by forging. For example, the convex portion 27 may be formed by cutting a cylindrical member that is larger than the body portion 21 .

The manufacturing method of the nut 20 of the present embodiment includes a cutting step S3 after the projection forming step S1. In the cutting step S3, a portion of the convex portion 27 is cut. A notch 28 shown in FIG. 8 is formed by cutting the convex portion 27 . The notch 28 is arranged on the back surface of the portion of the inner peripheral surface of the body portion 21 where the ball circulation groove 25 is formed. When viewed from the radial direction, the notch 28 overlaps a portion of the inner peripheral surface of the body portion 21 where the ball circulation groove 25 is formed.

The manufacturing method of the nut 20 of this embodiment includes a forging step S5 after the cutting step S3. In the forging step S<b>5 , the ball circulation grooves 25 are formed in the inner peripheral surface of the body portion 21 . In the forging step S5, as shown in FIGS. 8 and 9, a constraining die 81, a lower die 83, an upper die 85, a case 91, a tool 93, and a convex die 95 are used.

As shown in FIG. 8 , the constraining die 81 is arranged so as to cover the outer peripheral surfaces of the body portion 21 and the convex portion 27 . The constraining mold 81 constrains the outer peripheral surfaces of the body portion 21 and the convex portion 27 . Lower die 83 is arranged to cover one end face of nut 20 . The lower die 83 constrains the lower end surfaces of the main body portion 21 and the convex portion 27 . The upper die 85 is arranged so as to cover the other end surfaces of the body portion 21 and the convex portion 27 . The upper die 85 constrains the upper end surfaces of the main body portion 21 and the convex portion 27 .

As shown in FIG. 8 , the case 91 is arranged inside the body portion 21 . The case 91 is cylindrical and has a vertical hole 911 and a horizontal hole 913 . The vertical hole 911 is a hole penetrating from one end surface of the case 91 to the other end surface. The lateral hole 913 is a hole that connects the outer peripheral surface and the inner peripheral surface of the case 91 . As shown in FIG. 9, the tool 93 is a rod-shaped member such as a mandrel. A tool 93 is inserted into the vertical hole 911 . The tool 93 has a beveled surface 939 at the end that is inserted into the vertical hole 911 .

As shown in FIG. 8 , the convex mold 95 is arranged inside the body portion 21 . The convex mold 95 is arranged in the lateral hole 913 of the case 91 . The convex mold 95 can slide radially along the inner wall of the lateral hole 913 . The convex mold 95 has a protrusion 953 and a slope 959 . The protrusion 953 has a shape corresponding to the ball circulation groove 25 . The protrusion 953 is substantially S-shaped. A slope 959 is arranged behind the projection 953 .

As shown in FIG. 9, the tool 93 is inserted into the vertical hole 911 of the case 91 in the forging step S5. The tool 93 is then moved axially. When the slope 939 of the tool 93 comes into contact with the slope 959 of the convex mold 95, the convex mold 95 moves in the radial direction. When the protrusion 953 of the convex mold 95 is pressed against the inner peripheral surface of the main body 21, the inner peripheral surface is plastically deformed. Thereby, a ball circulation groove 25 is formed on the inner peripheral surface. Four ball circulation grooves 25 are formed one by one.

As shown in FIG. 9, as the ball circulation groove 25 is formed, a portion of the protrusion 27 is deformed. Specifically, the bottom surface of the notch 28 of the protrusion 27 is deformed. The depth of the notch 28 is greater than the height of the raised portion of the bottom surface of the notch 28 formed along with the ball circulation groove 25 . That is, the raised portion of the bottom surface of the notch 28 formed along with the ball circulation groove 25 does not extend beyond the outer peripheral surface of the convex portion 27 . Thereby, for example, when the protrusion 27 is guided by a guide groove provided in a member that supports the nut 20, the nut 20 can slide smoothly with respect to the guide groove. That is, the raised portion formed on the back side of the ball circulation groove 25 is less likely to get caught in the guide groove.

Through the forging step S5, the nut 20 having the ball circulation grooves 25 on the rear surface of the projection 27 is manufactured. In the manufactured nut 20 , the convex portion 27 has machining marks 271 . The machining mark 271 is a mark left on the surface of the convex portion 27 by forming the notch 28 in the cutting step S3. The machining marks 271 can also be said to be cutting marks formed on the convex portion 27 in the cutting step S3. Although the working marks 271 are deformed by the forging step S5, they remain on the surface of the convex portion 27 even after the forging step S5.

After manufacturing the nut 20, the ball screw 10 is manufactured. After manufacturing the nut 20, the nut 20, the screw shaft 40 and the ball 60 are assembled. That is, the method of manufacturing the ball screw 10 of the present embodiment includes an assembly step of assembling the nut 20, the screw shaft 40 and the balls 60 after manufacturing the nut 20. As shown in FIG.

In addition, in the nut 20 , the convex portion 27 does not necessarily have to be provided over the entire axial length of the body portion 21 . The convex portion 27 may be provided only partly over the entire length of the main body portion 21 in the axial direction. The number of protrusions 27 is not necessarily four, and is not particularly limited. The nut 20 only needs to have at least one protrusion 27 . The number of ball circulation grooves 25 is not necessarily four, and is not particularly limited. The nut 20 only needs to have at least one ball circulation groove 25 .

When the nut 20 has a plurality of ball circulation grooves 25, it is desirable that the ball circulation grooves 25 are arranged at equal intervals in the circumferential direction when viewed from the axial direction. The balls 60 in the ball circulation groove 25 cannot bear the load. By distributing the ball circulation grooves 25 in the circumferential direction, the areas where the balls 60 that cannot bear the load are disposed are distributed. If the nut 20 has a plurality of ball circulation grooves 25 , it is desirable that the number of protrusions 27 is greater than the number of ball circulation grooves 25 . Thereby, it is possible to arrange the ball circulation grooves 25 on the rear surface of the protrusion 27 in a one-to-one correspondence. A plurality of ball circulation grooves 25 may be arranged on the back surface of one projection 27 . As a result, the number of protrusions 27 formed in the protrusion forming step S1 can be reduced.

The notch 28 formed in the cutting step S3 does not necessarily have to have the shape shown in FIG. The depth of the notch 28 may be smaller than the height of the raised portion of the bottom surface of the notch 28 formed along with the ball circulation groove 25 . That is, the raised portion of the bottom surface of the notch 28 formed along with the ball circulation groove 25 may exceed the outer peripheral surface of the convex portion 27 (may protrude from the outer peripheral surface of the convex portion 27). In this case, it is desirable that part of the raised portion of the bottom surface of the notch 28 formed along with the ball circulation groove 25 be cut after the forging step S5. Thereby, for example, when the protrusion 27 is guided by a guide groove provided in a member that supports the nut 20, the nut 20 can slide smoothly with respect to the guide groove.

As described above, the nut 20 of the ball screw 10 of the present embodiment includes a cylindrical body portion 21, a thread groove 23 disposed on the inner peripheral surface of the body portion 21, and an inner peripheral surface of the body portion 21. and a ball circulation groove 25 arranged in the groove 23 and deeper than the thread groove 23 ; The ball circulation groove 25 is arranged behind the protrusion 27 . A length P1 of the projections 27 in the circumferential direction of the body portion 21 is smaller than a length P2 of the projections 27 in the axial direction of the body portion 21 .

By arranging the ball circulation groove 25 behind the convex portion 27, the wall thickness of the peripheral portion of the ball circulation groove 25 of the nut 20 is increased. That is, the distance from the surface of the ball circulation groove 25 to the outer peripheral surface of the nut 20 is increased. Therefore, the strength of the peripheral portion of the ball circulation groove 25 of the nut 20 is improved. As a result, when the nut 20 is subjected to heat treatment (quenching and tempering), the possibility of deformation and cracking of the nut 20 is reduced. In addition, since the length P1 of the protrusion 27 in the circumferential direction is smaller than the length P2 of the protrusion 27 in the axial direction, even if the ball circulation groove 25 is arranged behind the protrusion 27, the ball can be formed by forging. The circulation groove 25 can be easily formed. Therefore, the nut 20 of the ball screw 10 can improve the strength of the nut 20 and can easily form the ball circulation groove 25 .

In the nut 20 of the ball screw 10 of the present embodiment, the bottom 251 of the ball circulation groove 25 is arranged outside the outer peripheral surface of the body portion 21 in the radial direction of the body portion 21 .

As a result, the nut 20 of the ball screw 10 can be increased in thickness in the peripheral portion of the ball circulation groove 25 of the nut 20, and can be made smaller.

In the nut 20 of the ball screw 10 of the present embodiment, the length P1 of the protrusion 27 in the circumferential direction is smaller than the length P3 of the ball circulation groove 25 in the circumferential direction.

This makes it easier to form the ball circulation groove 25 by forging even if the ball circulation groove 25 is arranged behind the projection 27 . The nut 20 of the ball screw 10 can form the ball circulation groove 25 more easily.

In the nut 20 of the ball screw 10 of this embodiment, the convex portion 27 has processing marks 271 on its surface.

Forming the ball circulation groove 25 becomes easier by providing the notch 28 in the projection 27 before forming the ball circulation groove 25 . A processing mark 271 is a mark left on the surface of the convex portion 27 by forming the notch 28 .

In the method of manufacturing the nut 20 of the ball screw 10 of the present embodiment, a length P1 in the circumferential direction of the body portion 21 is smaller than a length P2 in the axial direction of the body portion 21 on the outer peripheral surface of the cylindrical body portion 21. A projection forming step S1 for forming the projections 27 and a forging step S5 for forming the ball circulation grooves 25 by pressing a projection die 95 against the rear surface of the projections 27 are provided.

By arranging the ball circulation groove 25 behind the convex portion 27, the wall thickness of the peripheral portion of the ball circulation groove 25 of the nut 20 is increased. That is, the distance from the surface of the ball circulation groove 25 to the outer peripheral surface of the nut 20 is increased. Therefore, the strength of the peripheral portion of the ball circulation groove 25 of the nut 20 is improved. As a result, when the nut 20 is subjected to heat treatment (quenching and tempering), the possibility of deformation and cracking of the nut 20 is reduced. In addition, since the length P1 of the convex portion 27 in the circumferential direction is smaller than the length P2 of the convex portion 27 in the axial direction, even when the convex mold 95 is pressed against the back surface of the convex portion 27 to form the ball circulation groove 25, , the ball circulation groove 25 can be easily formed. Therefore, the method of manufacturing the nut 20 of the ball screw 10 of the present embodiment can improve the strength of the nut 20 and easily form the ball circulation grooves 25 .

The method for manufacturing the nut 20 of the ball screw 10 of the present embodiment includes a cutting step S3 for cutting a part of the convex portion 27 after the convex portion forming step S1 and before the forging step S5.

Cutting a part of the projection 27 before forming the ball circulation groove 25 makes it easier to form the ball circulation groove 25 . The method of manufacturing the nut 20 of the ball screw 10 of this embodiment can form the ball circulation groove 25 more easily.

10 Ball screw 11 Rolling path 20 Nut 21 Main body 23 Thread groove 25 Ball circulation groove 27 Convex part 28 Notch 40 Screw shaft 43 Thread groove 60 Ball 81 Constraint die 83 Lower die 85 Upper die 91 Case 93 Tool 95 Convex die 251 Bottom 271 Machining marks 911 Vertical hole 913 Horizontal hole 939 Slanted surface 953 Projection 959 Slanted surface S1 Projection formation process S3 Cutting process S5 Forging process Z Rotational axis

Claims (5)

a cylindrical main body;
a thread groove arranged on the inner peripheral surface of the main body;
a ball circulation groove arranged on the inner peripheral surface of the main body and deeper than the thread groove;
a convex portion arranged on the outer peripheral surface of the main body;
with
The ball circulation groove is arranged behind the protrusion,
the length of the projection in the circumferential direction of the body is smaller than the length of the projection in the axial direction of the body;
The length of the protrusion in the circumferential direction is smaller than the length of the ball circulation groove in the circumferential direction.
ball screw nut. a cylindrical main body;
a thread groove arranged on the inner peripheral surface of the main body;
a ball circulation groove arranged on the inner peripheral surface of the main body and deeper than the thread groove;
a convex portion arranged on the outer peripheral surface of the main body;
with
The ball circulation groove is arranged behind the protrusion,
the length of the projection in the circumferential direction of the body is smaller than the length of the projection in the axial direction of the body;
A notch is provided in a part of the convex part,
The notch is arranged on the back surface of the portion where the ball circulation groove is formed,
The bottom surface of the notch is provided with a protruding portion that protrudes from the bottom surface,
The depth of the notch is greater than the height of the ridge
ball screw nut. 2. The ball screw nut according to claim 1 , wherein the convex portion has machining marks on its surface. The ball screw nut according to any one of claims 1 to 3, wherein the bottom of the ball circulation groove is arranged outside the outer peripheral surface of the main body in the radial direction of the main body. a protrusion forming step of forming a protrusion whose length in the circumferential direction of the main body is smaller than the length in the axial direction of the main body on the outer peripheral surface of the cylindrical main body;
a forging step of pressing a convex mold against the back surface of the convex portion to form a ball circulation groove;
with
A cutting step of cutting a part of the convex portion is provided after the convex portion forming step and before the forging step.
A method of manufacturing a ball screw nut.

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