WO2024252513A1 - Ball screw device - Google Patents

Abstract

A ball screw device 10 comprises: a screw shaft 11 formed with a first spiral groove 15; a nut 12 having a second spiral groove 16 and a through-hole 18; a plurality of balls 13 disposed on a rolling passage 17 formed between the first spiral groove 15 and the second spiral groove 16; a piece 14 provided in the through-hole 18 of the nut 12; and a cylindrical pressing member 19 fitted to an outer peripheral surface 12c of the nut 12. The piece 14 includes: a circulation groove 23 formed on an inner surface 22a on an inner side in a radial direction, for returning and circulating the balls 13 from a downstream side to an upstream side of the rolling passage 17; and a protruding portion 24 that is provided on an outer surface 21a on an outer side in the radial direction, protrudes radially outward beyond the outer peripheral surface 12c of the nut 12, and contacts an inner peripheral surface 19a of the pressing member 19. The protruding portion 24 is provided at a position where centers X1, X2 of contact areas R1, R2 of the protruding portion 24 with the inner peripheral surface 19a of the pressing member 19 do not overlap with the circulation groove 23 when the nut 12 is viewed from the outside in the radial direction.

Description

Ball screw device

The present invention relates to a ball screw device.

Patent Document 1 discloses a top-type ball screw device that uses a top as a circulating part. This ball screw device includes a screw shaft with a spiral rolling groove on its outer periphery, a cylindrical nut with a spiral rolling groove on its inner periphery, multiple balls, and multiple tops. The multiple balls are arranged to be able to roll in the rolling path formed by the rolling grooves of both the screw shaft and the nut. Multiple support holes are formed in the peripheral wall of the nut, penetrating it in the radial direction.

The multiple pieces are fitted into each support hole of the nut. A circulation groove (circulation path) is formed inside the piece to return the multiple balls to a designated position in the rolling path and circulate them. A radially outward load is generated on the piece by the balls passing through the circulation groove. For this reason, a cylindrical pressing member (holding member) is fitted into the outer periphery of the nut to prevent the piece from slipping out of the nut's support hole. The inner circumferential surface of the pressing member comes into contact with a protrusion protruding from the outer surface of the piece, thereby pressing the piece from the radially outward direction.

JP 2016-114185 A

In the ball screw device, the protrusion of the top is located at a radially outward position in the circulation groove. Therefore, if the protrusion is pressed strongly by the pressing member, the circulation groove may be deformed, and the ball circulation function of the top may be reduced.

The present disclosure aims to provide a ball screw device that can prevent the ball circulation function of the top from deteriorating even when the top is pressed by a pressing member.

The ball screw device of the present disclosure comprises a screw shaft having a first spiral groove formed on its outer periphery, a cylindrical nut surrounding the screw shaft, a second spiral groove formed on its inner periphery facing the first spiral groove, and a through hole formed radially penetrating its peripheral wall, a plurality of balls arranged in a rolling path formed between the first spiral groove and the second spiral groove, a top provided in the through hole of the nut, and a ball bearing that is fitted onto the outer periphery of the nut and presses the top provided in the through hole from the outside in the radial direction. and a cylindrical pressing member, the top has a circulation groove formed on the inner surface of the inner side in the radial direction for circulating the balls by returning them from the downstream side of the rolling path to the upstream side, and a protrusion provided on the outer surface of the outer side in the radial direction, protruding outward in the radial direction beyond the outer surface of the nut and contacting the inner surface of the pressing member, and the protrusion is provided at a position where the center of the contact area of the protrusion with the inner surface of the pressing member does not overlap with the circulation groove when the nut is viewed from the outside in the radial direction.

According to the present disclosure, even if the top is pressed by the pressing member, it is possible to prevent the ball circulation function of the top from being reduced.

1 is a schematic cross-sectional view of a ball screw device according to an embodiment. FIG. 2 is a side view of a nut of the ball screw device. FIG. 2 is a side view of a top of the ball screw device. FIG. 2 is a plan view of the top as seen from the radially inner side. 11A and 11B are diagrams illustrating a contact state between a first protrusion and a pressing member. 13A and 13B are diagrams illustrating a contact state between a second protrusion and a pressing member.

First, the contents of the embodiment will be listed and described.
<Overview of the embodiment>
(1) A ball screw device according to an embodiment of the present invention includes a screw shaft having a first spiral groove formed on an outer periphery thereof, a cylindrical nut arranged to surround the screw shaft, a second spiral groove formed on an inner periphery thereof facing the first spiral groove, and a through hole formed by penetrating a peripheral wall in a radial direction, a plurality of balls arranged in a rolling path formed between the first spiral groove and the second spiral groove, a top provided in the through hole of the nut, and a pressure roller fitted on an outer periphery of the nut to press the top provided in the through hole from the outside in the radial direction. and a cylindrical pressing member which is inserted into the nut and presses the nut against the nut, the top having a circulation groove formed on the inner surface of the inner side in the radial direction for circulating the balls by returning them from the downstream side to the upstream side of the rolling path, and a protrusion provided on the outer surface of the outer side in the radial direction, protruding radially outward beyond the outer surface of the nut and in contact with the inner surface of the pressing member, the protrusion being provided at a position such that, when the nut is viewed from the outside in the radial direction, the center of a contact area of the protrusion with the inner surface of the pressing member does not overlap with the circulation groove.

In the above-mentioned ball screw device, when the pressing member is fitted onto the outer peripheral surface of the nut, the protruding portion of the top provided in the through hole of the nut comes into contact with the inner peripheral surface of the pressing member and is pressed from the radially outward direction by the pressing member. At that time, when the nut is viewed from the radially outward direction, the center of the contact area of the protruding portion with the pressing member, i.e., the position of the protruding portion that is pressed most strongly by the pressing member, does not overlap with the circulation groove of the top. This makes it possible to suppress deformation of the circulation groove when the top is pressed by the pressing member, and therefore to suppress a decrease in the ball circulation function of the top.

(2) In the ball screw device described in (1) above, the through hole has an inner hole portion that opens on the inner peripheral surface of the nut, and an outer hole portion that is larger than the inner hole portion and opens on the outer peripheral surface of the nut, the nut further has a step surface that is provided at least in a portion of the connection between the inner hole portion and the outer hole portion and faces in the radial direction, the top further has an abutment surface that abuts against the step surface, and the protrusion is preferably provided at a position where at least a portion of the contact area overlaps with the abutment surface when the nut is viewed from the outside in the radial direction.

In this case, when the nut is viewed from the outside in the radial direction, at least a part of the contact area of the protruding portion of the top with the pressing member overlaps with the abutment surface of the top. This allows the pressing force of the pressing member against the top to be received by the stepped surface of the nut via the abutment surface of the top. As a result, deformation of the circulation groove when the top is pressed by the pressing member can be further suppressed.

(3) In the ball screw device described in (2), the top has the circulation groove extending in a predetermined direction, the protrusion includes a first protrusion provided on one side of the predetermined direction on the outer surface and a second protrusion provided on the other side of the predetermined direction on the outer surface, the step surface includes a first step surface formed on one side of the predetermined direction at the connection point and a second step surface formed on the other side of the predetermined direction at the connection point, and the abutment surface abuts against the first step surface. The nut preferably includes a first contact surface that contacts the inner circumferential surface of the pressing member and a second contact surface that contacts the second step surface, and the first protrusion is provided at a position where at least a part of the contact area of the first protrusion with the inner circumferential surface of the pressing member overlaps with the first contact surface when the nut is viewed from the outside in the radial direction, and the second protrusion is preferably provided at a position where at least a part of the contact area of the second protrusion with the inner circumferential surface of the pressing member overlaps with the second contact surface when the nut is viewed from the outside in the radial direction.

In this case, the first and second protrusions provided on the outer surface of the top on both sides of the longitudinal direction (predetermined direction) of the circulation groove each come into contact with the inner peripheral surface of the pressing member. This allows the top to be reliably pressed from the radially outward direction by the pressing member. In addition, the pressing force of the pressing member against the first and second protrusions can be received by the first and second step surfaces of the nut via the first and second abutment surfaces of the top, respectively. As a result, even if the first and second protrusions are pressed by the pressing member, deformation of the circulation groove can be effectively suppressed.

(4) In the ball screw device according to any one of (1) to (3), it is preferable that a surface of the protrusion is formed into a curved shape.
In this case, since the inner peripheral surface of the pressing member comes into contact with the surface of the protruding portion that is formed in a curved shape, the pressing member can be smoothly fitted onto the outer peripheral surface of the nut.

<Details of the embodiment>
Hereinafter, preferred embodiments will be described with reference to the drawings.
[Ball screw device]
1 is a schematic cross-sectional view of a ball screw device 10 according to an embodiment. The ball screw device 10 is used, for example, in a brake device of a vehicle (automobile). The ball screw device 10 includes a screw shaft 11, a nut 12, a plurality of balls 13, a plurality of tops 14, and a pressing member 19. The screw shaft 11 is connected to a driving device such as a motor (not shown). The driving device drives the screw shaft 11 to rotate around its own axis C. When the screw shaft 11 rotates, the nut 12 moves in a direction along the axis C of the screw shaft 11.

In this disclosure, the direction along the axis C of the screw shaft 11 is simply referred to as the "axial direction." The axial direction also includes a direction parallel to the axis C. A direction perpendicular to the axis C is simply referred to as the "radial direction." The direction in which the screw shaft 11 rotates around the axis C is simply referred to as the "circumferential direction."

The screw shaft 11 is formed in a cylindrical shape. A first spiral groove 15 is formed on the outer periphery of the screw shaft 11. The first spiral groove 15 is formed in a spiral shape over the entire axial direction of the screw shaft 11. The nut 12 is formed in a cylindrical shape. The nut 12 is disposed radially outward of the screw shaft 11, surrounding the screw shaft 11. The axis of the nut 12 coincides with the axis C of the screw shaft 11. A second spiral groove 16 is formed on the inner periphery of the nut 12. The second spiral groove 16 faces the first spiral groove 15 in the radial direction. The second spiral groove 16 is formed, for example, in a cross section of an arc.

A rolling path 17 along which the balls 13 roll is formed between the first spiral groove 15 of the screw shaft 11 and the second spiral groove 16 of the nut 12. A plurality of balls 13 are arranged in the rolling path 17. When the screw shaft 11 rotates, the balls 13 roll along the rolling path 17, thereby applying an axial force to the nut 12 and moving the nut 12 in the axial direction.

FIG. 2 is a side view of the nut 12. As shown in FIGS. 1 and 2, the nut 12 has through holes 18 formed radially penetrating its peripheral wall 12a. A plurality of through holes 18 are formed at intervals in the circumferential direction of the nut 12. In this embodiment, four through holes 18 (only two are shown in FIGS. 1 and 2) are formed at equal intervals of 90° in the circumferential direction of the nut 12. These through holes 18 are formed at different positions in the axial direction.

Each through hole 18 is formed long and in a direction inclined relative to the circumferential direction when viewed from the radial outside of the nut 12. The inclination direction of the through holes 18 relative to the circumferential direction of the nut 12 is opposite to the inclination direction of the second spiral groove 16 relative to the circumferential direction of the nut 12.

Each through hole 18 has an inner hole portion 18a and an outer hole portion 18b. The inner hole portion 18a is formed on the inner periphery side of the nut 12. The inner hole portion 18a opens at the inner periphery surface 12b of the nut 12. The outer hole portion 18b is formed on the outer periphery side of the nut 12. The outer hole portion 18b opens at the outer periphery surface 12c of the nut 12. The outer hole portion 18b is formed larger than the inner hole portion 18a.

A step surface 12d is formed around the entire circumference of the connection point between the inner hole portion 18a and the outer hole portion 18b of each through hole 18 in the nut 12. The step surface 12d faces in the radial direction. The step surface 12d includes a first step surface 12d1 (see FIG. 5) and a second step surface 12d2 (see FIG. 6). The first step surface 12d1 is formed on one side of the longitudinal direction of the through hole 18 at the connection point. The second step surface 12d2 is formed on the other side of the longitudinal direction of the through hole 18 at the connection point. Hereinafter, in this disclosure, when common features of the first step surface 12d1 and the second step surface 12d2 are described, they will be collectively referred to as step surface 12d.

The multiple pieces 14 are fitted into each of the through holes 18 of the nut 12. Details of the pieces 14 will be described later. The pressing member 19 is formed in a cylindrical shape and is fitted into the outer peripheral surface 12c of the nut 12. The inner peripheral surface 19a of the pressing member 19 presses the multiple pieces 14 fitted into each of the through holes 18 of the nut 12 from the outside in the radial direction. In this embodiment, the pressing member 19 is made of a metal material (e.g., cold-rolled steel plate such as SPCD).

[Top]
Fig. 3 is a side view of the top 14. Fig. 4 is a plan view of the top 14 as viewed from the inside in the radial direction. In Figs. 1, 3 and 4, the top 14 is formed, for example, by forging a metal material. The top 14 includes a head 21 and legs 22. The head 21 is formed in a shape that matches the outer hole portion 18b of the through hole 18 of the nut 12, and is fitted into the outer hole portion 18b. In this embodiment, the head 21 is formed in an elliptical shape as viewed from the outside in the radial direction.

The radially outer outer surface 21a of the head 21 is curved with approximately the same curvature as the outer peripheral surface 12c of the nut 12. The head 21 has an abutment surface 21b that abuts against the step surface 12d when fitted into the outer hole portion 18b. The abutment surface 21b is formed on the radially inner inner surface of the head 21, all around the leg portion 22.

The abutment surface 21b includes a first abutment surface 21b1 and a second abutment surface 21b2. The first abutment surface 21b1 is formed in an arc shape on the inner surface of one side in the longitudinal direction of the head 21 (left side in FIG. 4). When the top 14 is fitted into the through hole 18, the first abutment surface 21b1 abuts against the first step surface 12d1. The second abutment surface 21b2 is formed in an arc shape on the inner surface of the other side in the longitudinal direction of the head 21 (right side in FIG. 4). When the top 14 is fitted into the through hole 18, the second abutment surface 21b2 abuts against the second step surface 12d2. Hereinafter, in this disclosure, when common features of the first abutment surface 21b1 and the second abutment surface 21b2 are described, they are collectively referred to as abutment surface 21b.

The legs 22 of the top 14 are integrally formed on the inner surface of the head 21. The legs 22 are formed in a shape that matches the inner hole 18a of the through hole 18 of the nut 12, and are fitted into the inner hole 18a. The inner surface 22a on the radially inner side of the legs 22 is curved in a side view so as to approach the head 21 from both longitudinal ends toward the center.

A circulation groove 23 is formed on the inner surface 22a of the leg 22. The circulation groove 23 is a groove for circulating the balls 13 by returning them from the downstream side of the rolling path 17 to the upstream side. The circulation groove 23 is recessed toward the head 21 and is formed with an arc-shaped cross section. The circulation groove 23 extends over the entire longitudinal direction (predetermined direction) of the leg 22. The circulation groove 23 meanders gently from one longitudinal end to the other. The circulation groove 23 is formed deepest in the central part in the longitudinal direction.

An inlet 22b is formed at one longitudinal end of the leg 22, which introduces the balls 13 from the rolling path 17 to the circulation groove 23. An outlet 22c is formed at the other longitudinal end of the leg 22, which returns the balls 13 from the circulation groove 23 to the rolling path 17. When the leg 22 is fitted into the inner bore 18a, the inlet 22b is located in one of the axially adjacent groove portions in the first spiral groove 15 of the screw shaft 11, and the outlet 22c is located in the other groove portion.

As shown in FIG. 1, the balls 13 move from the upstream side to the downstream side of the rolling path 17 due to the rotation of the screw shaft 11, and when they reach the position of the top 14, they are introduced into the circulation groove 23 from the inlet 22b. The balls 13 introduced into the circulation groove 23 move along the circulation groove 23 and are returned to the upstream side of the first spiral groove 15 from the outlet 22c. As a result, the balls 13 circulate through the rolling path 17, allowing the nut 12 to move smoothly in the axial direction relative to the screw shaft 11.

[Protrusion]
2 to 4, the top 14 has a pair of protrusions 24 provided on the outer surface 21a of the head 21. The pair of protrusions 24 includes a first protrusion 241 and a second protrusion 242. The first protrusion 241 is integrally formed on an end of the outer surface 21a on one side in the longitudinal direction (the left side in FIG. 3). The second protrusion 242 is integrally formed on an end of the outer surface 21a on the other side in the longitudinal direction (the right side in FIG. 3). Hereinafter, in this disclosure, when common features of the first protrusion 241 and the second protrusion 242 are described, they will be collectively referred to as protrusion 24.

The surface 24a of the protrusion 24 is curved when viewed from the side of the top 14 in the axial direction. When the head 21 is fitted into the outer hole 18b, the surface 24a of the protrusion 24 protrudes radially outward beyond the outer circumferential surface 12c of the nut 12. The surface 24a of the protrusion 24 is also formed to extend in the axial direction when the head 21 is fitted into the outer hole 18b. In this state, when the pressing member 19 is fitted into the outer circumferential surface 12c of the nut 12, the surface 24a of the protrusion 24 comes into contact with the inner circumferential surface 19a of the pressing member 19.

FIG. 5 is a diagram illustrating the contact state between the first protrusion 241 and the pressing member 19. The upper diagram in FIG. 5 is a plan view of the first protrusion 241 viewed from the outside in the radial direction. The lower diagram in FIG. 5 is a side view of the first protrusion 241. In FIG. 5, the surface 24a of the first protrusion 241 has a contact region R1 (the region shown by cross-hatching and single hatching in the upper diagram in FIG. 5) that contacts the inner circumferential surface 19a of the pressing member 19. When the contact region R1 comes into contact with the inner circumferential surface 19a of the pressing member 19, it is deformed so as to be crushed radially inward.

The center X1 of the contact area R1 of the first protrusion 241 is located in a position that does not overlap with the circulation groove 23 when viewed from the radial outside. In this embodiment, the center X1 of the contact area R1 is located further outward in the longitudinal direction of the top 14 than the circulation groove 23 (on the left side of Figure 5). In addition, a portion R1a of the contact area R1 (the area shown by cross-hatching in the upper diagram of Figure 5) is located in a position that overlaps with the first abutment surface 21b1 when viewed from the radial outside. In this embodiment, the portion R1a of the contact area R1 occupies more than half of the area of the contact area R1, including the center X1.

FIG. 6 is a diagram illustrating the contact state between the second protrusion 242 and the pressing member 19. The upper diagram in FIG. 6 is a plan view of the second protrusion 242 viewed from the outside in the radial direction. The lower diagram in FIG. 6 is a side view of the second protrusion 242. In FIG. 6, the surface 24a of the second protrusion 242 has a contact region R2 (the region shown by cross-hatching and single hatching in the upper diagram in FIG. 6) that contacts the inner circumferential surface 19a of the pressing member 19. When the contact region R2 comes into contact with the inner circumferential surface 19a of the pressing member 19, it is deformed so as to be crushed radially inward.

The center X2 of the contact area R2 of the second protrusion 242 is located in a position that does not overlap with the circulation groove 23 when viewed from the radial outside. In this embodiment, the center X2 of the contact area R2 is located further outward in the longitudinal direction of the top 14 than the circulation groove 23 (to the right in Figure 6). In addition, a portion R2a of the contact area R2 (the area shown by cross-hatching in the upper diagram in Figure 6) is located in a position that overlaps with the second abutment surface 21b2 when viewed from the radial outside. In this embodiment, the portion R2a of the contact area R2 occupies more than half of the area of the contact area R2, including the center X2.

[Effects of the embodiment]
According to the ball screw device 10 of this embodiment, when the pressing member 19 is fitted into the outer circumferential surface 12c of the nut 12, the protrusion 24 of the top 14 provided in the through hole 18 of the nut 12 comes into contact with the inner circumferential surface 19a of the pressing member 19 and is pressed from the radially outward direction by the pressing member 19. At that time, when the nut 12 is viewed from the radially outward direction, the centers X1, X2 of the contact areas R1, R2 of the protrusion 24 with the pressing member 19, i.e., the positions of the protrusion 24 that are pressed most strongly by the pressing member 19, do not overlap with the circulation groove 23 of the top 14. This makes it possible to suppress deformation of the circulation groove 23 when the top 14 is pressed by the pressing member 19, and therefore to suppress a decrease in the circulation function of the top 14 for the balls 13.

When the nut 12 is viewed from the outside in the radial direction, portions R1a, R2a of the contact regions R1, R2 in the protruding portion 24 of the top 14 overlap the abutment surface 21b of the top 14. This allows the pressing force of the pressing member 19 against the top 14 to be received by the step surface 12d of the nut 12 via the abutment surface 21b of the top 14. As a result, deformation of the circulation groove 23 when the top 14 is pressed by the pressing member 19 can be further suppressed.

The outer surface 21a of the top 14 is provided with a first protrusion 241 and a second protrusion 242 on both sides of the circulation groove 23 in the longitudinal direction. As a result, the first protrusion 241 and the second protrusion 242 are in contact with the inner circumferential surface 19a of the pressing member 19, respectively, so that the top 14 can be reliably pressed from the radially outward direction by the pressing member 19. In addition, the pressing force of the pressing member 19 against the first protrusion 241 and the second protrusion 242 can be received by the first step surface 12d1 and the second step surface 12d2 of the nut 12 via the first abutment surface 21b1 and the second abutment surface 21b2 of the top 14, respectively. As a result, even if the first protrusion 241 and the second protrusion 242 are pressed by the pressing member 19, deformation of the circulation groove 23 can be effectively suppressed.

When protrusions 24 are provided on both sides of the circulation groove 23 in the short direction on the outer surface 21a of the top 14, it is necessary to increase the width of the head 21 of the top 14 in the short direction to ensure space for providing these protrusions 24. Increasing the width of the head 21 increases the width of the abutment surfaces 21b on both sides of the head 21 in the short direction. Accordingly, it is necessary to increase the width of the step surfaces 12d on both sides of the short direction of the nut 12, which increases the machining allowance of the step surfaces 12d in the nut 12. In contrast, the protrusions 24 in this embodiment are provided on both sides of the circulation groove 23 in the longitudinal direction, so the machining allowance of the step surfaces 12d in the nut 12 can be reduced.

The surface 24a of the protrusion 24 is curved. This allows the inner circumferential surface 19a of the pressing member 19 to come into contact with the surface 24a of the protrusion 24, allowing the pressing member 19 to be smoothly fitted onto the outer circumferential surface 12c of the nut 12.

[others]
The embodiments disclosed above are illustrative in all respects and are not restrictive. For example, the ball screw device 10 has been described as being used in a brake device, but it can also be applied to other devices. The number of the tops 14 is not limited to this embodiment. The step surface 12d of the nut 12 is formed around the entire circumference of the connection between the inner hole portion 18a and the outer hole portion 18b, but it is sufficient that the step surface 12d is provided on at least a part of the connection.

The surface 24a of the protrusion 24 is formed in a curved shape, but is not limited to this. For example, the surface 24a of the protrusion 24 may be formed in a trapezoid shape. The protrusions 24 are provided on both sides in the longitudinal direction of the outer surface 21a of the top 14, but may be provided on only one side or only the other side in the longitudinal direction. The protrusions 24 may also be provided on both sides in the lateral direction of the outer surface 21a of the top 14, or may be provided on only one side or only the other side in the lateral direction.

In this embodiment, portions R1a, R2a of the contact regions R1, R2 of the protrusion 24 are positioned to overlap the abutment surface 21b of the top 14, but this is not limited to this. For example, the entire contact regions R1, R2 may be positioned so as not to overlap the abutment surface 21b. Also, the entire contact regions R1, R2 may be positioned so as to overlap the abutment surface 21b.

REFERENCE SIGNS LIST 10 ball screw device 11 screw shaft 12 nut 12a peripheral wall 12b inner peripheral surface 12c outer peripheral surface 12d step surface 12d1 first step surface 12d2 second step surface 13 ball 14 top 15 first spiral groove 16 second spiral groove 17 rolling path 18 through hole 18a inner hole portion 18b outer hole portion 19 pressing member 19a inner peripheral surface 21a outer surface 21b abutment surface 21b1 first abutment surface 21b2 second abutment surface 21c protrusion 22a inner surface 23 circulation groove 24 protrusion 24a outer surface 241 first protrusion 242 second protrusion R1, R2 contact area R1a, R2a part X1, X2 Center

Claims (4)

a screw shaft having a first spiral groove formed on an outer periphery thereof;
A cylindrical nut is disposed around the screw shaft, and has a second spiral groove formed on an inner periphery thereof facing the first spiral groove, and a through hole formed radially penetrating a peripheral wall thereof;
a plurality of balls disposed in a rolling path formed between the first spiral groove and the second spiral groove;
A top provided in the through hole of the nut;
a cylindrical pressing member that is fitted to an outer peripheral surface of the nut and presses the top provided in the through hole from the outside in the radial direction,
The top is:
a circulation groove formed on the inner surface on the inside in the radial direction for circulating the balls by returning them from the downstream side to the upstream side of the rolling path;
A protrusion is provided on an outer surface on the outside in the radial direction, protruding outward in the radial direction beyond an outer peripheral surface of the nut, and contacting an inner peripheral surface of the pressing member.
the protrusion is provided at a position such that, when the nut is viewed from the outside in the radial direction, the center of the contact area of the protrusion with the inner surface of the pressing member does not overlap with the circulation groove. The through hole is
An inner hole portion that opens to an inner peripheral surface of the nut;
An outer hole portion is formed larger than the inner hole portion and opens on an outer peripheral surface of the nut,
The nut further has a stepped surface provided at at least a portion of a connection between the inner hole portion and the outer hole portion and facing in the radial direction,
The top further has an abutment surface that abuts against the step surface,
The ball screw device according to claim 1 , wherein the protrusion is provided at a position where at least a portion of the contact area overlaps with the abutment surface when the nut is viewed from the outside in the radial direction. The top has the circulation groove extending in a predetermined direction,
the protrusion includes a first protrusion provided on one side of the outer surface in the predetermined direction and a second protrusion provided on the outer surface on the other side of the predetermined direction,
the step surface includes a first step surface formed on one side in the predetermined direction at the connection portion and a second step surface formed on the other side in the predetermined direction at the connection portion,
the abutment surface includes a first abutment surface that abuts against the first step surface and a second abutment surface that abuts against the second step surface,
The first protrusion is provided at a position where, when the nut is viewed from the outside in the radial direction, at least a part of a contact area of the first protrusion with the inner circumferential surface of the pressing member overlaps with the first abutment surface,
3. The ball screw device according to claim 2, wherein the second protrusion is provided at a position where, when the nut is viewed from the radial outside, at least a part of a contact area of the second protrusion with the inner circumferential surface of the pressing member overlaps with the second abutment surface. The ball screw device according to any one of claims 1 to 3, wherein the surface of the protrusion is curved.

Images